Abscisic acid (ABA) is a phytohormone that plays an essential regulatory role in a variety of physiological processes, including embryo development, seed dormancy, transpiration, and adaptation to environmental stresses. ABA regulates many agronomically important aspects of plant development including synthesis of seed storage proteins and lipids as well as regulation of stomatal closure. The analysis of ABA-responsive promoters has revealed a diversity of potential cis-acting regulatory elements.
Mutations in genes impacting ABA biosynthesis and signaling are known in several plant species. See, for example, Leung and Giraudat, (1998) Annu. Rev. Plant Physiol. Plant Mol. Biol. 49:199-222, and the references cited therein. In Arabidopsis, a number of genetically distinct Arabidopsis acid-insensitive loci have been identified. These mutants were selected based on the ability of seeds to germinate in the presence of inhibitory concentrations of ABA. The mutations have also been shown to affect several additional aspects of seed development, including accumulation of storage proteins and lipids, chlorophyll breakdown, desiccation tolerance, and embryonic maturation. In addition, ABA-mediated growth control is a fundamental response of plants to adverse environmental conditions. Methods are needed to modulate the response of plants to ABA, particularly for mitigating effects of abiotic stress on vegetative and/or reproductive growth in order to maintain or increase yield.